In recent years, because of the improvement of living standard, diabetes, obesity and cardiovascular diseases increase by years, and a younger-age trend occurs. Therefore, the development of a lower-energy multifunctional sweetener with nutritional properties is becoming a focal issue of consumers.
Difructose anhydride III is a novel functional sweetener, of which the structure is mainly formed by removing two water molecules from two fructose molecules. Since all hydroxyl groups in anomeric carbon become glycosidic bonds, the difructose anhydride III is a novel non-reducing disaccharide. Because of the existence of such a special form of diglycosidic bonds, the difructose anhydride III has very stable properties. The difructose anhydride III is quite stable for heat and acids, can resist high temperature, and cannot generate the phenomenon of browning or decomposition during high-temperature processing of common food. The sweetness of the difructose anhydride III is only ½ that of sucrose, but the heat is lower than that of sucrose, and is only 1/15 that of sucrose (0.263 kcal/g), so the difructose anhydride III has good functions for patients with diabetes and obesity; and therefore, the difructose anhydride III can be used as an ideal sucrose substitute in low-energy food and diabetic food for preventing and treating diabetes. In the meanwhile, the difructose anhydride III has lower hydroscopicity than the sucrose, and does not absorb moisture under the relative humidity of 74%, thereby facilitating the storage of sugar. The difructose anhydride III cannot be absorbed by the intestinal tract, thus cannot generate energy, and therefore, can be used as a sweetener for adjuvant therapy of weight loss. Although the difructose anhydride III cannot be directly digested and absorbed by the intestinal tract of the human body, the difructose anhydride III can be utilized and metabolized by probiotics in the intestinal tract to generate abundant prebiotics, thereby promoting growth of probiotics in the human body and good health of the human body. The difructose anhydride III can promote the absorption of calcium, magnesium, zinc, copper and other mineral elements as well as flavonoids by the human body, and thus, has the effects of promoting bone growth, etc. Dental caries is mainly caused by corrosion of teeth due to acids produced by sucrose and other saccharides as streptococcus mutans metabolize in a cavity. However, the difructose anhydride cannot be metabolized by the streptococcus mutans, and thus, has the effect of inhibiting dental caries. Besides, the difructose anhydride III has multiple physiological functions of lowering cholesterol, high blood pressure and the like. In view of the favorable properties of the difructose anhydride III, the difructose anhydride III can be used as a food additive in bakery food, beverages, candies, etc. Therefore, the difructose anhydride III has broad prospects in food industry.
The difructose anhydride exists in the natural world, mainly in compositae, such as cichorium intybus, Jerusalem artichoke, etc., but is lower in content. Besides, a small amount of difructose anhydride III also exists in processing of honey, coffee, etc. The content of the difructose anhydride III is lower in the natural world, so the cost for extracting and separating difructose anhydride III is very high. Although the difructose anhydride III can be produced by chemical methods, the chemical synthesis methods have many adverse factors, such as environmental pollution, etc. The difructose anhydride can also be obtained by a biological catalysis method. In 1973, Uchiyama T detected inulin fructotransferase (EC 4.2.2.18) in Arthrobacter ureafaciens for the first time, and after that, it has been detected that a dozen of microorganisms can generate inulin fructotransferase. The bioconversion method has the advantages of wide raw material sources, low price, high conversion rate and suitability for industrial production. However, in all existing methods, the difructose anhydride III is obtained by directly converting plant inulin, which firstly requires plant inulin; and inulin has higher price than sucrose, so the existing methods are not economically efficient.
The inventor provides a method using cheaper sucrose as a substrate: the sucrose is firstly converted into inulin by inulosucrase, and the synthesized biological inulin is directly converted into difructose anhydride III by inulin fructotransferase; and in this process, the separation and purification of the inulin are not required, thereby reducing the energy consumption and lowering production cost; and finally, other saccharides existing in a reaction solution are removed by yeast to obtain the purer difructose anhydride III, thereby facilitating the subsequent separation and purification.